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Topologically Heterogeneous Beta Cell Adaptation in
Response to High-Fat Diet in Mice
Johanne H. Ellenbroek1, Hendrica A. Töns1, Natascha de Graaf1, Cindy J. Loomans2, Marten A. Engelse1,
Hans Vrolijk3, Peter J. Voshol4, Ton J. Rabelink1, Françoise Carlotti1, Eelco J. de Koning1,2*
1 Department of Nephrology, Leiden University Medical Center, Leiden, The Netherlands, 2 Hubrecht Institute, Utrecht, The Netherlands, 3 Department of Molecular Cell
Biology, Leiden University Medical Center, Leiden, The Netherlands, 4 Institute of Metabolic Science, University of Cambridge, Cambridge, United Kingdom
Abstract
Aims: Beta cells adapt to an increased insulin demand by enhancing insulin secretion via increased beta cell function and/or
increased beta cell number. While morphological and functional heterogeneity between individual islets exists, it is
unknown whether regional differences in beta cell adaptation occur. Therefore we investigated beta cell adaptation
throughout the pancreas in a model of high-fat diet (HFD)-induced insulin resistance in mice.
Methods: C57BL/6J mice were fed a HFD to induce insulin resistance, or control diet for 6 weeks. The pancreas was divided
in a duodenal (DR), gastric (GR) and splenic (SR) region and taken for either histology or islet isolation. The capacity of
untreated islets from the three regions to adapt in an extrapancreatic location was assessed by transplantation under the
kidney capsule of streptozotocin-treated mice.
Results: SR islets showed 70% increased beta cell proliferation after HFD, whereas no significant increase was found in DR
and GR islets. Furthermore, isolated SR islets showed twofold enhanced glucose-induced insulin secretion after HFD, as
compared with DR and GR islets. In contrast, transplantation of islets isolated from the three regions to an extrapancreatic
location in diabetic mice led to a similar decrease in hyperglycemia and no difference in beta cell proliferation.
Conclusions: HFD-induced insulin resistance leads to topologically heterogeneous beta cell adaptation and is most
prominent in the splenic region of the pancreas. This topological heterogeneity in beta cell adaptation appears to result
from extrinsic factors present in the islet microenvironment.
Citation: Ellenbroek JH, Töns HA, de Graaf N, Loomans CJ, Engelse MA, et al. (2013) Topologically Heterogeneous Beta Cell Adaptation in Response to High-Fat
Diet in Mice. PLoS ONE 8(2): e56922. doi:10.1371/journal.pone.0056922
Editor: Kathrin Maedler, University of Bremen, Germany
Received August 10, 2012; Accepted January 16, 2013; Published February 18, 2013
Copyright: ß 2013 Ellenbroek et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by the Diabetes Cell Therapy Initiative consortium including the Dutch Diabetes Research Foundation. The funders had no
role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: [email protected]
histological studies in human pancreas describe a higher islet
density in the tail compared to the body region of the pancreas
[4,9,10].
While morphological and functional heterogeneity between
individual islets exists, it is unknown whether there are regional
differences in beta cell adaptation throughout the pancreas.
Regional heterogeneity in cell proliferation rate is observed in
regenerating liver lobules after partial hepatectomy [11]. In this
study, we examine early events of beta cell adaptation in different
regions of the pancreas using a model of high-fat diet induced
insulin resistance in mice that is known to increase beta cell mass
in the long term [12,13].
Introduction
The insulin producing pancreatic beta cells are essential to
maintain blood glucose levels within a narrow range. When the
demand for insulin is chronically increased by physiological or
pathological changes, beta cells can adapt by enhancing insulin
secretion via increased beta cell function and/or increased beta
cell mass [1,2]. Inadequate adaptation leads to the development of
hyperglycemia and eventually diabetes mellitus [3,4]. Therefore,
insight into the mechanisms that control beta cell adaptation is
important for developing therapies that can preserve or enhance
beta cell mass.
The pancreas is a regionally heterogeneous organ. During
embryonic development the pancreas originates from two
epithelial buds. The ventral bud gives rise to the posterior part
of the head and the uncinate process, and the dorsal bud forms the
anterior part of the head, the body and the tail of the pancreas
[5,6]. Pancreatic islets derived from the ventral bud contain more
cells producing pancreatic polypeptide (PP), whereas islets derived
from the dorsal bud contain more alpha cells and secrete more
insulin upon glucose stimulation [7,8]. Furthermore, several
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Research Design and Methods
Animals
Male C57BL/6J mice, 8 weeks old (Charles River Laboratories,
Wilmington, MA, USA) were fed a high-fat diet (HFD, 45 kcal%
fat, D12451, Research Diets, New Brunswick, NJ, USA) or a
normal diet (control, 10 kcal% fat, D12450B, Research Diets) for 6
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Topologically Heterogeneous Beta Cell Adaptation
Figure 1. Metabolic characteristics of control mice and mice fed a high fat diet for 6 weeks. A. Body weight (n = 13–14 mice). B. Food
intake (n = 4 cages). C. Blood glucose concentrations during GTT (n = 6 mice). D. AUC blood glucose concentrations during GTT (n = 6 mice). E. Insulin
concentrations during GTT (n = 5–6 mice). F. AUC insulin concentrations during GTT (n = 5–6 mice). G. Blood glucose concentrations during ITT (n = 8
mice). H. AUC of glucose concentrations during ITT (n = 8 mice). HFD = high-fat diet, AUC = area under the curve. *p,0.05, **p,0.01, ***p,0.001.
doi:10.1371/journal.pone.0056922.g001
weeks. Average food intake was determined per cage housing 3–4
mice weekly. For the 12-week diet study, 12 week old male
C57BL/6J mice (Animal Facility Leiden University Medical
Center), that were fed a high-fat or normal diet, were used. For
islet transplantation experiments we used male C57BL/6J donor
and recipient mice, 8–10 weeks old and fed regular chow. Animal
experiments were approved by the ethical committee on animal
care and experimentation of the Leiden University Medical
Center (Permit Numbers: 09174, 07145, and 11146).
was defined as the section of the pancreas attached to the
duodenum, the gastric region as the part attached to the pylorus
and stomach and the splenic region as the part attached to the
spleen. For immunohistochemistry each pancreatic region was
fixed in a random orientation in 4% paraformaldehyde and
embedded in paraffin. For islet isolation the pancreas of 6–8 mice
were pooled per region and digested using 3 mg/ml collagenase
(Sigma-Aldrich, St Louis, CA, USA). Islets were manually picked
and tested for insulin secretion or purified by gradient separation
(1.077 g/ml ficoll, hospital pharmacy, LUMC) and transplanted
after overnight culture.
Glucose and insulin tolerance test
An intra-peritoneal glucose tolerance test (GTT) was performed
in overnight-fasted mice. Blood samples were drawn from the tail
vein before injecting 2 g/kg glucose and after 15, 30, 60 and 120
minutes. An intra-peritoneal insulin tolerance test (ITT) was
performed in animals that had been fasted for 6 hours. After
measuring basal blood glucose concentration from the tail vein
0.75 U/kg insulin was injected followed by monitoring of the
blood glucose concentrations after 15, 30 and 60 minutes. Blood
glucose concentrations were measured using a glucose meter
(Accu-Chek, Roche, Basel, Switzerland) and insulin concentrations
were measured in 5 ml plasma samples by ELISA (Ultra Sensitive
Mouse Insulin ELISA kit, Chrystal Chem, Downers Grove, IL,
USA).
RNA preparation and real-time PCR
Total RNA was extracted from isolated islets using RNeasy
micro kit (Qiagen, Hilden, Germany) according to the manufacturer’s protocol. Total RNA (400 ng) was reverse transcribed using
M-MLV reverse transcriptase (Invitrogen). Quantitative PCR
(qPCR) was performed on a CFX384 Real-Time PCR Detection
System (Bio-Rad Laboratories, Hercules, CA, USA) using the
SYBR Green PCR Master Mix (Applied Biosystems, Foster city,
CA, USA). Fold induction was calculated using deltaCT method
with mouse cyclophilin as housekeeping gene. Mouse primers used
were: cyclophilin (forward) 5’-CAGACGCCACTGTCGCTTT-3’
and (reverse) 5’-TGTCTTTGGAACTTTGTCTGCAA-3’; cyclin
D1 (forward) 5’- TCCGCAAGCATGCACAGA-3’ and (reverse)
5’-GGTGGGTTGGAAATGAACTTCA-3’; insulin 2 (forward)
5’-CTGGCCCTGCTCTTCCTCTGG-3’
and
(reverse)
5’CTGAAGGTCACCTGCTCCCGG-3’.
Pancreas dissection and islet isolation
The pancreas was dissected, weighed and based on their spatial
relation to adjacent organs divided into three parts: the duodenal,
gastric and splenic region (Fig. S1) [14,15]. The duodenal region
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Topologically Heterogeneous Beta Cell Adaptation
Figure 2. Beta cell mass morphometry in control and HFD mice. A. Beta cell mass in the entire pancreas after 6 weeks (n = 6 mice). B. Beta cell
mass by pancreatic region after 6 weeks (n = 6 mice per region). C. Beta cell cluster area in the entire pancreas after 6 weeks (n = 6 mice). D. Beta cell
cluster area by pancreatic region after 6 weeks (n = 6 mice per region). E. Islet density in the entire pancreas after 6 weeks (n = 6 mice). F. Islet density
by pancreatic region after 6 weeks (n = 6 mice per region). G. Beta cell area in the entire pancreas after 12 weeks (n = 6 mice). H. Beta cell area by
pancreatic region after 12 weeks (n = 6 mice per region). DR = duodenal region, GR = gastric region, SR = splenic region, HFD = high-fat diet.
*p,0.05, #p,0.05 by unpaired Student’s t test.
doi:10.1371/journal.pone.0056922.g002
capsule. The peritoneum and the skin were sutured and the
animals were allowed to recover under a warm lamp. Blood
glucose concentrations were monitored every other day after
transplantation via blood from the tail vein. The islet graft was
removed 10 days post-transplantation, fixed by immersion in a 4%
paraformaldehyde solution, embedded in paraffin blocks and
sliced into 4 mm sections and mounted on slides.
Glucose-induced insulin secretion
Groups of 10 islets were incubated in a modified Krebs-Ringer
Bicarbonate buffer (KRBH) containing 115 mM NaCl, 5 mM
KCl, 24 mM NaHCO3, 2.2 mM CaCl2, 1 mM MgCl2, 20 mM
HEPES, 2 g/l human serum albumin (Cealb, Sanquin, The
Netherlands), pH 7.4. Islets were successively incubated for 1 hour
in KRBH with 2 mM and 20 mM glucose at 37uC. Insulin
concentration was determined in the supernatants by ELISA
(Mercodia, Uppsala, Sweden). Insulin secretion was corrected for
DNA content to correct for islet size differences. DNA content was
determined by Quant-iT PicoGreen dsDNA kit (Invitrogen,
Carlsbad, CA, USA).
Beta cell mass morphometry and proliferation
For the identification of beta cells, sections were immunostained
with guinea-pig anti-insulin IgG (Millipore, Billerica, MA, USA) or
rabbit anti-insulin IgG (Santa Cruz Biotechnology, Santa Cruz,
CA, USA) for 1 hour followed by HRP- or AP- conjugated
secondary antibodies for 1 hour. Sections were developed with
3,3’-diaminobenzidine tetrahydrochloride (DAB) or liquid permanent red (LPR, Dako, Denmark) and counterstained with
hematoxylin.
For determining the beta cell mass, 3-4 insulin-DAB stained
sections (200 mm apart) per pancreatic region were digitally
imaged (Panoramic MIDI, 3DHISTECH, Hungary). Beta cell
area and pancreas area stained with hematoxylin were determined
using an image analysis program (Stacks 2.1, LUMC), excluding
large blood vessels, larger ducts, adipose tissue and lymph nodes.
The area of clusters containing $4 beta cells was individually
measured and used to determine the average beta cell cluster area
per pancreatic region. Islet density was determined by dividing the
number of beta cell clusters by the (regional) area that was
analyzed. Beta cell mass was determined by the percentage of beta
Islet transplantation
For islet transplantation experiments recipient mice were made
diabetic by intra-peritoneal injection of 160 mg/kg streptozotocin
(STZ, Sigma-Aldrich), freshly dissolved in citrate buffer (pH 4.5).
Mice were considered diabetic when the blood glucose concentration was greater than 20 mmol/L. Blood glucose concentrations were determined in blood obtained from the tail vein by a
glucose meter (Accu-Chek). Prior to the transplantation mice were
given 0.1 mg/kg buprenorfin (Temgesic, Schering-Plough, Kenilworth, NJ) after which they were anaesthetized using isoflurane
and kept warm on a heating pad. The left kidney was exposed by a
small opening in the flank of the mouse. A small incision was made
in the kidney capsule. Using a Hamilton syringe (Hamilton
Company, Reno, CA) and polyethylene tubing (PE50, Becton
Dickinson, Franklin Lakes, NJ) siliconized with Sigmacote (SigmaAldrich), 150 islets per mouse were transplanted under the kidney
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Topologically Heterogeneous Beta Cell Adaptation
Figure 3. Beta cell proliferation in control and HFD mice after 6 weeks. A. Image of proliferating beta-cells (arrowheads), Ki67 (green), insulin
(red) and DAPI (blue). Scale bar = 50 mm. B. Image of proliferating beta-cells (arrowheads), BrdU (brown) and insulin (red) per pancreatic region in
control and HFD mice. Mice received BrdU during the final 7 days. Scale bar = 50 mm. C. Beta cell proliferation in the entire pancreas, BrdU labeling
during the final 7 days (n = 6 mice). D. Beta cell proliferation by pancreatic region, BrdU labeling during the final 7 days (n = 6 mice per region). E.
Cyclin D1 mRNA expression by pancreatic region, control = 1. DR = duodenal region, GR = gastric region, SR = splenic region, HFD = high-fat diet.
*p,0.05, ***p,0.001
doi:10.1371/journal.pone.0056922.g003
phate nick end labeling (TUNEL) assay (Roche). The investigator
was blind to the experimental conditions.
cell area to pancreas (regional) area multiplied by the pancreas
(regional) weight.
Two techniques were used to identify proliferating beta cells.
First, incorporation of 5-bromo-29-deoxyuridine (BrdU, SigmaAldrich) in proliferating beta cells was established by administering
50 mg/kg BrdU subcutaneously twice daily during the final 7 days
of the 6-week study period. The transplanted recipient mice
received 1 mg/ml BrdU in the drinking water (refreshed every
other day) during the final 7 days. Sections were double stained for
insulin-LPR and BrdU (BrdU staining kit, Invitrogen). BrdUpositive beta cells were assessed as a proportion of all beta cells per
pancreatic region or islet graft. Second, sections were double
stained with goat anti-Ki67 IgG (Santa Cruz Biotechnology) and
guinea-pig anti-insulin IgG (Millipore) overnight at 4uC after heatinduced antigen retrieval in 0.01 M citrate buffer (pH 6.0)
followed by biotin-conjugated anti-goat IgG (Dako), streptavidine-Alexa 488 (Invitrogen) and TRITC-conjugated anti-guineapig (Jackson ImmunoResearch Laboratories, West Grove, PA,
USA). Nuclei were stained with DAPI (Vector Laboratories,
Burlingame, CA, USA). Apoptotic beta-cells were counted after
being identified by immunostaining for insulin and by the terminal
deoxynucleotidyl-transferase-mediated deoxyuridine 5-triphosPLOS ONE | www.plosone.org
Statistical analysis
Data are presented as means 6 SEM. Statistical calculations
were carried out using GraphPad Prism 5 (GraphPad Software,
San Diego, CA, USA). The statistical significance of differences
was determined by an unpaired Student’s t test or two-way
ANOVA, followed by Bonferroni’s multiple comparisons test, as
appropriate. P,0.05 was considered statistically significant.
Results
Metabolic characteristics of mice fed HFD for 6 weeks
Body weight and food intake were increased after 6 weeks HFD
compared to control (Fig. 1A, B). After overnight fasting glucose
concentrations were similar (5.160.2 mmol/L (HFD) vs
5.060.2 mmol/L (control), p = 0.72). Glucose tolerance was
decreased in HFD mice compared to control (Fig. 1C, D),
whereas insulin concentrations were increased twofold (Fig. 1E, F).
Insulin tolerance was decreased by HFD (Fig. 1G, H). Therefore,
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Topologically Heterogeneous Beta Cell Adaptation
Figure 4. Glucose-induced insulin secretion from isolated islets of control and HFD mice. Insulin secretion was corrected for DNA content.
A. Insulin secretion during 2 mM and 20 mM glucose stimulation from islets in the entire pancreas (n = 24). B. Insulin secretion from islets by
pancreatic region during incubation in 2 mM glucose buffer (n = 8 per region) and C. 20 mM glucose buffer (n = 8 per region) for control and HFD
mice. D. Insulin mRNA expression by pancreatic region, control = 1. DR = duodenal region, GR = gastric region, SR = splenic region, HFD = high-fat
diet. *p,0.05, **p,0.01, ***p,0.001.
doi:10.1371/journal.pone.0056922.g004
HFD for 6 weeks is sufficient to induce insulin resistance leading to
an increased demand for insulin from beta cells.
increase the sensitivity for detecting proliferating beta cells, BrdU
was administered for 7 days. We counted 885648 beta cells per
region per mouse. Beta cell proliferation was significantly
increased in HFD mice compared to control mice (Fig. 3C). A
positive correlation was found between the increase in body weight
and the rate of beta cell proliferation in HFD mice (r2 = 0.70;
p,0.05) (data not shown). HFD increased beta cell proliferation by
70% in the SR of the pancreas whereas no significant increase was
found in the DR and GR (Fig. 3B, D). Also mRNA levels of Cyclin
D1 were increased in islets from the splenic region of HFD mice
(Fig. 3E). By counting on average 460673 cells per region per
mouse, the occurrence of apoptotic beta cells was very low and not
different between the two groups (data not shown).
Increased beta cell proliferation in the splenic region of
the pancreas in response to HFD
The effect of HFD on early beta cell adaptation in different
regions was evaluated. The pancreas was divided in three regions:
a duodenal, gastric and splenic region. The beta cell mass was
determined by analyzing 29.961.6 mm2 pancreatic tissue per
region per mouse. A difference in beta cell mass between HFD and
control mice was found neither in the entire pancreas, nor in the
separate regions (Fig. 2A, B). For determination of the average
beta cell cluster area 4662.5 clusters were included per region.
The beta cell cluster area was significantly larger in islets from the
GR, no differences were found between HFD and control mice
(Fig. 2C, D). Islet density was homogeneous throughout the
pancreas and similar after HFD for 6 weeks (Fig. 2E, F). After 12
weeks HFD we could confirm an increased beta-cell area, which
was mostly augmented in the SR of the pancreas compared to
control mice (Fig. 2G, H).
For determination of the number of proliferating beta cells
Ki67+ beta cells were counted in 9566 islets per mouse (Fig. 3A).
The occurrence of Ki67+/insulin+ cells was very low (Ki67+/
Insulin+ 0.1260.03% (HFD) vs. 0.0960.02% (control)). To
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Prominent increase in glucose-induced insulin release
from isolated islets in the splenic region by HFD
The functional adaptation of islets from HFD mice was assessed
by measurement of glucose-induced insulin secretion. Stimulation
of islets from HFD mice with 20 mM glucose led to a twofold
increase in insulin secretion compared to control mice (Fig. 4A).
When comparing the response of islets derived from the different
pancreatic regions after HFD, insulin secretion was 56% and 72%
higher in SR islets compared to GR and DR islets, respectively
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Topologically Heterogeneous Beta Cell Adaptation
Figure 5. Beta cell adaptation in islets grafts from different pancreatic regions transplanted in syngeneic diabetic mice. A. Average
islet size per transplant. B. Blood glucose concentrations of STZ-induced diabetic mice followed up to 10 days after transplantation (n = 6–8 mice per
region) of DR, GR or SR islets. C. AUC blood glucose concentrations post-transplantation corrected for pre-transplantation glucose concentration
(n = 6–8 mice per region). D. Image of proliferating beta-cells, positive for both BrdU (brown) and insulin (red) in islets transplanted under the kidney
capsule of diabetic mice. Scale bar = 20 mm. E. Beta cell proliferation in the islet grafts 10 days after transplantation, BrdU labeling during the final 7
days (n = 6–7 mice per region). DR = duodenal region, GR = gastric region, SR = splenic region, AUC = area under the curve.
doi:10.1371/journal.pone.0056922.g005
and 2 out of 8 SR islet grafts. On average, all transplants led to a
similar decrease in hyperglycemia (blood glucose concentrations
10 days post-transplantation 11.561.6 mmol/L (DR grafts),
15.562.1 mmol/L (GR grafts), 15.761.7 (SR grafts) mmol/L,
p = 0.20; Fig. 5B, C). For determination of the number of
proliferating beta cells in the grafts 11146113 beta cells per islet
graft were counted. Beta cell proliferation was similar for DR, GR
or SR islet grafts (p = 0.53, Fig. 5D, E).
(Fig. 4B, C). Expression levels of Insulin mRNA showed a similar
pattern (Fig. 4D).
Similar islet function and beta cell proliferation after
transplantation of islets from different regions to an
extrapancreatic location
Next we assessed whether the observed proliferative and
functional islet heterogeneity is due to differences in the islet
microenvironment or due to intrinsic differences between islets
from the three regions. Islets isolated from the three pancreatic
regions were transplanted under the kidney capsule of syngeneic
STZ-induced diabetic mice. All grafts contained 150 handpicked
islets with an average size of that was similar for all transplants
resulting in a similar graft size (Fig. 5A). Since hyperglycemia in
these mice is required for detectable adaptation of grafted islets
[16,17], the increased demand for insulin in this model is expected
to be a potent stimulus for beta cell adaptation in the islet graft.
The islet graft size was sufficient to reduce blood glucose
concentrations, but it was not sufficient to lead to normoglycemia
in most mice thereby maintaining the stimulus for beta cells to
adapt [17]. Normoglycemia (defined as blood glucose concentration ,10 mmol/L) was reached with 3 out of 7 DR, 1 out of 6 GR
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Discussion
The main results of our study show that beta cell adaptation is
topologically heterogeneous throughout the pancreas. Splenic
islets are involved in the first line of response in beta cell
adaptation. Although morphological and functional heterogeneity
between individual islets have been described before, this is the
first study showing regional differences in beta cell adaptation to
an increased metabolic demand.
Beta cell adaptation in different pancreatic regions was studied
in mice fed HFD for 6 weeks. We hypothesized that this time
period would be long enough to induce metabolic changes and
would allow us to investigate early islet adaptation. Six weeks HFD
led to insulin resistance, with a higher demand for insulin to which
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February 2013 | Volume 8 | Issue 2 | e56922
Topologically Heterogeneous Beta Cell Adaptation
beta cells started to adapt. Since beta cell mass was not
significantly changed yet, but an increased rate of beta cell
proliferation was already observed, this is an appropriate model
for studying early events of beta cell adaptation.
The presence of increased beta cell proliferation and an
augmented insulin secretory response in islets derived from the
splenic region of the pancreas indicates that islets in this part of the
pancreas constitute an early line of defense against an increased
insulin demand. Our study was not designed to answer whether
the relative contribution of beta cell adaptation in the different
regions changes during prolonged high-fat feeding.
The observed proliferative and functional heterogeneity between islets from different regions in response to a HFD stimulus
could be explained in two ways: either the islets from different
pancreatic regions are intrinsically different or they receive distinct
extrinsic signals from their microenvironment. This latter hypothesis was investigated by transplanting isolated islets to an
extrapancreatic location in diabetic mice. After 10 days, islet
grafts from the duodenal, gastric or splenic region led to a similar
decrease in hyperglycemia and there was no difference in beta cell
proliferation. Therefore we suggest that this newly identified
topological heterogeneity of beta cell adaptation observed in HFD
mice is most likely the result of distinct extrinsic signals present in
the microenvironment of the islet.
The islet microenvironment is formed by a complex network of
nerves and blood vessels that mediate neuronal, humoral and
circulatory signals which are involved in beta cell adaptation. Islets
are densely innervated by the autonomic nervous system [18] and
it was reported that beta cell mass adaptation is regulated by
neuronal signals from the liver [19]. A recent study identified a
subpopulation (5%) of islets with greater blood perfusion and
vascular density, which was associated with increased beta cell
function and proliferation [20]. But it still remains unclear whether
the increased vascular density is the cause or the consequence of
the increased beta cell mass. Another possible factor is the strong
paracrine dialogue between the islet microvasculature and beta
cells [21]. However, here we show that early adaptation persists in
vitro after isolation of the islets, since SR islets from HFD mice
display an enhanced glucose-induced insulin secretion compared
to DR and GR islets. Therefore, this indicates that heterogeneity
in beta cell adaptation is not dependent on immediate innervation
or vascular blood supply.
Furthermore, a strong structural and functional relationship
between islets and acinar cells exists, which is referred to as the
islet-acinar axis, in which insulin and somatostatin play an
important role in regulating exocrine function [22]. It was shown
that the amylase content of acinar tissue from the splenic region of
rats is higher than in the duodenal region of the pancreas [23].
Whether the exocrine tissue surrounding islets can locally
influence beta cell adaptation remains an open question.
Past studies have shown that islets from the dorsal pancreas
secrete more insulin compared to islets from the ventral region
[8,24]. The gastric and splenic regions originate from the dorsal
lobe. However our data also show heterogeneous adaptation
within the dorsal pancreas (GR vs SR) indicating that embryonic
origin of the different regions does not entirely explain the
heterogeneity observed in this study.
It is likely that our findings of regional heterogeneity in beta cell
adaptation can be extended to the human pancreas. In the
pancreas of humans and non-human primates heterogeneity in
islet density throughout the pancreas [4,9,10], and changes in islet
mass associated with different metabolic conditions have been
described [3,25–29]. For patients undergoing distal pancreatectomy, this would imply loss of the most adaptive islets which may
lead to a higher risk for postoperative diabetes. Furthermore,
histological studies of beta cell adaptation in the human pancreas
are often based on tissue samples from the splenic region only
[3,25], whereas this may not be representative for the entire organ.
Finally, the findings of this study imply that the islet
microenvironment harbors factors that are involved in beta cell
adaptation. Investigation of these regional differences may lead to
the identification of factors that play a key role in beta cell
regeneration.
Supporting Information
Figure S1 The spatial relation to adjacent organs was
used to divide the pancreas into three parts: DR =
duodenal region, GR = gastric region, SR = splenic
region.
(TIF)
Acknowledgments
The authors thank Jacques Duijs for technical assistance and Maarten
Ellenbroek for the illustration shown in Fig. S1.
Author Contributions
Conceived and designed the experiments: JHE CJL MAE HV PJV TJR
FC EJK. Performed the experiments: JHE HAT NG. Analyzed the data:
JHE FC EJK. Contributed reagents/materials/analysis tools: HV PJV.
Wrote the paper: JHE CJL MAE TJR FC EJK.
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